A detailed knowledge of the processes involved during the determination of the primordial germ cells is needed before a comprehensive understanding of cell determination of this specific cell type can be obtained. Our principal goals have been to clarify the normal development of pole cells in Drosophila and then to elucidate the defects which appear in mutations specifically affecting these cells. In addition, we have continue exploratory analysis of normal Drosophila development, maternal effect mutations affecting gastrulation, and finally some specific processes of cogenesis. In specific, we will complete the analysis of the fate of 3H-thymidine labelled pole cells, transplanted into unlabeled embryos. We will continue our analysis of the maternal effect lethal mutation, 573, which affects both mesoderm formation during gastrulation and the formation of the labrum. Finally, we will determine the characteristics of the in vitro synthesized vitellogenins and compare them to vitellogenine isolated from fly abdomens. We will attempt to identify recombinant DNA molecules containing the vitellogenin genes. By in situ hybridization we will determine the cytogenetic locus of the genes.